Subject: Re: [linux-audio-dev] LAAGA - main components
From: Abramo Bagnara (abramo_AT_alsa-project.org)
Date: Mon Apr 30 2001 - 19:51:58 EEST
Paul Davis wrote:
>
> >- if we need for some reasons to use poll(2) or select(2) between
> >components of the full system, we have to use something useable with
> >poll/select (by example AF_LOCAL sockets).
>
> thats the whole point. you can't have multiple process communicating
> via OS objects if you want low latency (reliably). the components in
> the system must be in the same process.
Why do you think I want to? Nothing in pcm_shm/pcm_lbserver model forces
multiple process, nothing forces to have OS objects for communicating.
> if you don't agree with me, then i would like to see a working example
> of this design with a 1.3msec deadline for audio processing.
I've not a strong opinion for or against this statement, perhaps you're
right, perhaps it's an urban myth, who knows ;-)
However it's definitely irrelevant as the model I propose *do not* force
task scheduling every elapsed period.
> the entire audio processing part of the system has to effectively run
> in interrupt context; since this is Unix, we don't do that literally,
> but we do the next best thing: we use an RT_FIFO thread on a low
> latency system, which poll(2)'s the relevant file descriptor(s). it
> will run within 0.25msec of the interrupt about 99.5% of the time (or
> better).
And so what? We're discussing about the API for component communication,
we are not discussing whether to use a single thread, multiple threads
or multiple processes.
-- Abramo Bagnara mailto:abramo_AT_alsa-project.orgOpera Unica Phone: +39.546.656023 Via Emilia Interna, 140 48014 Castel Bolognese (RA) - Italy
ALSA project http://www.alsa-project.org It sounds good!
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